Kohler COMMAND CH18-745 User Manual download pdf (Page 64)

5B.5

Section 5B

EFI Fuel System

Three different styles of ECU’s have been utilized in

EFI production. The first style is easily identified by its

metal case with large 35 pin connector block, and also

as MA 1.7. See Figure 5B-1. The second and third

styles have plastic cases, but are smaller in overall

size. These have either a 24 pin or 32 pin connector

block and identified as MSE 1.0 or MSE 1.1

respectively. See Figures 5B-2 and 5B-3. Basic

function and operating control remains the same

between the three, however, due to differences in the

internal circuitry as well as the wiring harness, none of

the ECU’s are interchangeable. Certain individual

service/troubleshooting procedures also apply, where

applicable, they are covered individually as: “35 Pin”

(MA 1.7) Metal-Cased ECU, “24 Pin” (MSE 1.0)

Plastic-Cased ECU, or “32 Pin” (MSE 1.1) Plastic-

Cased ECU.

General

The ECU is the brain or central processing computer

of the entire EFI fuel/ignition management system.

During operation, sensors continuously gather data

which is relayed through the wiring harness to input

circuits within the ECU. Signals to the ECU include:

ignition (on/off), crankshaft position and speed (RPM),

throttle position, oil temperature, exhaust oxygen

levels, and battery voltage. The ECU compares the

input signals to the programmed maps in its memory

to determine the appropriate fuel and spark

requirements for the immediate operating conditions.

The ECU then sends output signals to set the injector

duration and ignition timing.

The ECU continually performs a diagnostic check of

itself, each of the sensors, and the system

performance. If a fault is detected, the ECU turns on

the Malfunction Indicator Light (MIL) on the equipment

control panel, stores the fault code in its fault memory,

and goes into a default operating mode. Depending on

the significance or severity of the fault, normal

operation may continue, or “limp home” operation

(slowed speed, richer running) may be initiated. A

technician can access the stored fault code using a

“blink code” diagnosis flashed out through the MIL. An

optional computer software diagnostic program is also

available, order Kohler Part No. 25 761 23-S.

The ECU requires a minimum of 7.0 volts to operate.

The adaptive memory in the ECU is operational the

moment the battery cables are connected, however

the adapted values are lost if the battery becomes

disconnected for any reason. The ECU will “relearn”

the adapted values if the engine is operated for 10-15

minutes at varying speeds and loads after the oil

temperature exceeds 55°C (130°F).

To prevent engine over-speed and possible failure, a

“rev-limiting” feature is programmed into the ECU. If

the maximum RPM limit (4125 RPM on MA 1.7, 4500

RPM on MSE 1.0 & MSE 1.1) is exceeded, the ECU

suppresses the injection signals, cutting off the fuel

flow. This process repeats itself in rapid succession,

limiting operation to the preset maximum.

Service

Never attempt to disassemble the ECU. It is sealed to

prevent damage to internal components. Warranty is

void if the case is opened or tampered with in any way.

All operating and control functions within the ECU are

preset. No internal servicing or readjustment may be

performed. If a problem is encountered, and you

determine the ECU to be faulty, contact your source of

supply. Do not replace the ECU without factory

authorization.

The relationship between the ECU and the throttle

position sensor (TPS) is very critical to proper system

operation. If the TPS or ECU is changed, or the

mounting position of the TPS is altered, the applicable

“TPS Initialization Procedure” (see pages 5B.8 or

5B.9) must be performed to restore the

synchronization.

Engine Speed Sensor

Figure 5B-4. Engine Speed Sensor.

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Kohler COMMAND CH18-745 User Manual Page 64

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